"Tester" products found at beauty counters have been found to contain E.coli, staph and strep bacteria, the L.A. Times reports. A study conducted by Dr. Elizabeth Brooks, a biological sciences professor at Jefferson Medical College in Philadelphia, revealed that the percentage of tainted tester makeup--when analyzed on Saturdays, the business shopping day of the week--was a shocking 100%.

"We went to department stores, specialty stores, drugstores--everywhere. Wherever you see E. coli, you should just think 'E. coli equals feces.' That means someone went to the bathroom, didn't wash their hands and then stuck their fingers in that moisturizer," Brooks said.

And according to Dr. Zein Obagi, a dermatologist based in Beverly Hills, California, tester makeup can spread herpes and conjuctivitis.